<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<!-- <link rel="stylesheet" href="header.css">
	<link rel="stylesheet" href="content.css"> -->
	<!-- <link rel="stylesheet" href="main.css"> -->
	<style>
		*{
			padding: 0;
			margin: 0;
		}
		body{
			font-size: 14px;

		}
		ul{
			list-style: none;
		}
		a{
			text-decoration: none;
		}
		input{
			border: 0;
			outline: 0;
		}
		.father{
			width: 100%;
			height: 200px;
			background-color: red;
			position: relative;
		}
		.box{
			width: 400px;
			height: 100px;
			background-color: green;
			position: absolute;

			/**/
			left: 50%;
			margin-left: -200px;
		}


	</style>
</head>
<body>
	<div class="father">
		<div class="box"></div>
	</div>
	
</body>
</html>